As to what Jesus meant when he said, "It is finished", Here is your best clue, given by Jesus himself,
Luke 14:26 If any man come to me, and hate not his father, and mother, and wife, and children, and brethren, and sisters, yea, and his own life also, he cannot be my disciple.
27 And whosoever doth not bear his cross, and come after me, cannot be my disciple.
28 For which of you, intending to build a tower, sitteth not down first, and counteth the cost, whether he have sufficient to finish it?
29 Lest haply, after he hath laid the foundation, and is not able to finish it, all that behold it begin to mock him,
30 Saying, This man began to build, and was not able to finish.
31 Or what king, going to make war against another king, sitteth not down first, and consulteth whether he be able with ten thousand to meet him that cometh against him with twenty thousand?
32 Or else, while the other is yet a great way off, he sendeth an ambassage, and desireth conditions of peace.
33 So likewise, whosoever he be of you that forsaketh not all that he hath, he cannot be my disciple.
34 Salt is good: but if the salt have lost his savour, wherewith shall it be seasoned?
35 It is neither fit for the land, nor yet for the dunghill; but men cast it out. He that hath ears to hear, let him hear.
Now Gentleman, ponder that against the following:
Romans 9:22 What if God, willing to shew his wrath, and to make his power known, endured with much longsuffering the vessels of wrath fitted to destruction:
23 And that he might make known the riches of his glory on the vessels of mercy, which he had afore prepared unto glory,
24 Even us, whom he hath called, not of the Jews only, but also of the Gentiles?
25 ¶As he saith also in Osee, I will call them my people, which were not my people; and her beloved, which was not beloved.
26 And it shall come to pass, that in the place where it was said unto them, Ye are not my people; there shall they be called the children of the living God.
27 Esaias also crieth concerning Israel, Though the number of the children of Israel be as the sand of the sea, a remnant shall be saved:
28 For he will finish the work, and cut it short in righteousness: because a short work will the Lord make upon the earth.
29 And as Esaias said before, Except the Lord of Sabaoth had left us a seed, we had been as Sodoma, and been made like unto Gomorrha.
30 ¶What shall we say then? That the Gentiles, which followed not after righteousness, have attained to righteousness, even the righteousness which is of faith.
31 But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness.
32 Wherefore? Because they sought it not by faith, but as it were by the works of the law. For they stumbled at that stumblingstone;
33 As it is written, Behold, I lay in Sion a stumblingstone and rock of offence: and whosoever believeth on him shall not be ashamed.
What was finished, Gentleman, was the laying of the stone of stumbling so that Old system could end with a remnant of his people saved, salvation go out to the Gentiles, and the new watchtower of God begin to be built under a new and better covenant.
Gentleman, there at Luke 14:26-35, we see a reference to Jerusalem as the watchtower of God. God had committed it's building into the hands of men who proved unable to finish it. So that Jewish system which was as God's watchtower to the people now proved to loose it's salt and be valueless. 35 " It is neither fit for the land, nor yet for the dunghill; but men cast it out. He that hath ears to hear, let him hear."
Jesus words, "It is finished" refer specifically to that Old Law Covenant system being finished. The stone of stumbling was laid and they had completed their tripping.
Those words of Jesus have nothing to do with our sin and to use his words that way is wrong and causes the lala attitudes of people who take sin too lightly to falsely believe they have found justification for it.
That Old Covenant system ended, and after Jesus death and ascension it was now time to begin building the new watchtower to the people under a new and better covenant.
2 Corinthians 6:1 "We then, as workers together with him, beseech you also that ye receive not the grace of God in vain."
1 Corinthians 3:9 For we are labourers together with God: ye are God's husbandry, ye are God's building.
10 According to the grace of God which is given unto me, as a wise masterbuilder, I have laid the foundation, and another buildeth thereon. But let every man take heed how he buildeth thereupon.
11 ¶For other foundation can no man lay than that is laid, which is Jesus Christ.
12 Now if any man build upon this foundation gold, silver, precious stones, wood, hay, stubble;
13 Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is.
14 If any man's work abide which he hath built thereupon, he shall receive a reward.
15 If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
16 ¶Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you?
17 If any man defile the temple of God, him shall God destroy; for the temple of God is holy, which temple ye are.
18 ¶Let no man deceive himself. If any man among you seemeth to be wise in this world, let him become a fool, that he may be wise.
19 For the wisdom of this world is foolishness with God. For it is written, He taketh the wise in their own craftiness.
20 And again, The Lord knoweth the thoughts of the wise, that they are vain.
21 ¶Therefore let no man glory in men. For all things are yours;
22 Whether Paul, or Apollos, or Cephas, or the world, or life, or death, or things present, or things to come; all are yours;
23 And ye are Christ's; and Christ is God's.